In removing solvents from polymers in solution polymerization processes the usual practice is to flash concentrate the reactor effluent to about 12-16 weight percent rubber and then steam strip the concentrated solution, commonly in two stages. The polymer is precipitated as it enters the primary stripping zone and is maintained as an aqueous slurry during steam stripping, the polymer crumb still containing some solvent dissolved in the solid phase.
The principal disadvantage of the steam stripping step is the high steam consumption required to vaporize the solvent, a characteristic of ever increasing concern as the price of energy escalates. For example, a steam stripper operating somewhat above atmospheric pressure and removing cyclohexane solvent requires approximately one pound of steam for each three pounds of solvent in the overhead vapor. This steam is generally condensed against cooling water or ambient air in the subsequent solvent recovery step, a tremendous waste of energy.